Steerable memory alloy guide wires

ABSTRACT

A medical guide wire or the like that is comprised in part or entirely of one or more heat activated memory alloys alone or in conjunction with one or more non-heat activated memory materials. 
     The tip or any portion of a guide wire comprised of memory alloy or components thereof can be aimed, deflected or steered on command by applying heat to the alloy. Combining heat activated memory alloys alone or with non-heat activated memory materials in opposite or antagonistic configurations or assemblies permits reversible shape change of the guide wire in any direction. The heat activated or shape memory alloys may be titanium-nickel alloys, titanium-nickel-cobalt alloys, other transition and precious metal alloys or thermoplastic heat settable material which exhibit shape memory characteristics. Heating of the guide wire is accomplished by induction heating, immersion heating, application of RF energy, or by body temperature.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to guide wires which are steerable by reason ofshape memory materials used in their construction.

A guide wire is a medical device that is typically formed of a long,flexible metal wire coiled or uncoiled, and having one or morecomponents. They are generally used to gain access to a body structureor location by inserting it into the body and advancing it to thedesired location. The guide wire can be used to probe, biopsy,penetrate, dilate or act as a vehicle for transporting an accompanyingcatheter to a given location.

It is, of course, desirable to provide a readily insertable guide wirethat is also accurately steerable. Effective tip or body deflection ofthe wire, which provides the necessary steering capability, is importantso that the guide wire can be quickly and accurately steered and guidedthrough the desired path to the desired target structure or locationwithin the body. In the past, guide wire designs have either lackedactive steering capability, or they have incorporated mechanicalsteering designs which are large, awkward to use, and have limitedsteering characteristics. In this regard, typical guide wireconstructions are shown in U.S. Pat. Nos. 4,619,274; 4,545,390;4,538,622 and 3,528,406.

Quick, safe and effective steering of the guide wire is very importantin many medical applications, especially in angioplasty procedures. Forexample, in percutaneous transluminal coronary angioplasty (PTCA)procedures, an inflatable balloon catheter is used to dilate narrow(stenotic) lesion sites within coronary arteries. A guide wire usuallyprecedes an associated catheter by establishing passage through, andlocation of its distal tip at the site of the coronary artery narrowing,at which time the catheter is telescoped over the guide wire andadvanced to the desired area. It will be appreciated that the anatomy ofblood vessels in general, and especially so in coronary arteries, isvery circuitous, or tortuous, with many side branches that complicatethe successful passage of guide wires to their desired location. Thus,effective steering of the tip and/or body of the guide wire becomes veryimportant for the quick, safe and accurate passage and placement of theguide wire preceding the transport and location of the PTCA catheter.

It is to be understood that the concept of a steerable guide wire is notlimited to percutaneous transluminal coronary angioplasty (PTCA)procedures. Accurate steering capability is desirable in any guide wireused for any purpose such as, but not limited to, balloon and laserangioplasty, nephrostomy, angiography, electrode placement, etc.

SUMMARY OF THE INVENTION

The present invention provides a readily insertable and accuratelysteerable guide wire wherein the tip end, and/or selective body portionsof the guide wire are comprised, at least in part, of a shape memoryalloy. Shape memory alloys are those materials which exhibit mechanicalmemory triggered or activated by heat. Examples of such material are thetitanium-nickel alloy disclosed in U.S. Pat. No. 3,174,851 and U.S. Pat.No. 3,672,879, as well as the titanium-nickel cobalt alloy disclosed inU.S. Pat. No. 3,558,369. The first mentioned alloy consists essentiallyof from 52 to 56% nickel by weight and correspondingly from about 48 to44% titanium by weight. The alloy has the structure of a substantiallyTiNi phase from about 500° C. to about -75° C. This material isoriginally formed with restraint by annealing (typically at 950° to1100° F.) into the shape desired when inserted into the body (such as acurve, angle or any other of an infinite variety of single or multipleconfigurations). The material is then deformed at a temperature(typically room temperature), below its transitional temperature (fromabout 32° to about 331° F. depending upon relative composition, buttypically from 98° to 125° F.), into a shape facilitating easy insertioninto the body, for example, in the form of a straight rod. The materialis then incorporated into or attached to the guide wire structure.

When the guide wire is inserted into the body, the shape memory alloycan be activated on command by the application of heat to effect adeflection in the wire, enabling it to be steered in the desired path toits target location within the body.

Once heated to its transitional temperature, the shape memory alloymaterial will maintain its original shape even when cooled below itstransitional temperature, if no external antagonistic force is applied.

The titanium-nickel cobalt alloy (Nitinol™) disclosed in U.S. Pat. No.3,558,369, has the formula TiNi_(x) Co_(1--x) wherein Ti denotestitanium and constitutes approximately 50 atomic percent of thecomposition, and the term NI_(x) Co_(1--x) denotes nickel and cobaltrespectively and make up the remaining approximately 50 atomic percentof the composition. X is a factor which varies from greater than 0 toless than 1 whereby the relative percentage of nickel and cobalt variesinversely from less than 100% to more than 0%. The transitionaltemperature of this alloy can be varied depending upon relativecomposition from -396° to +331° F. Otherwise, it is essentially the sameas the above-mentioned titanium-nickel alloy.

It will be appreciated that shape memory materials other thantitanium-nickel alloys such as Nitinol™, may be effectively employed inthe present invention. Titanium-copper alloys may also be used, and itis known that many other alloys of the transition and precious metalsexhibit shape memory characteristics as well. Thermoplastic shape memorymaterials may also be used.

The present invention applies the shape memory alloy concept to provideaccurate steering capability to guide wires in various forms. Forexample, it is well known to form a guide wire as a tightly, helicallycoiled spring. According to this invention, a shape memory alloy elementis attached to the spring so as to extend beyond the distal tip of thespring. It is also contemplated to locate the shape memory alloy elementwithin the lumen of the spring, in the distal tip portion, and/or at alocation removed from the distal tip portion. In addition, while it ispreferred to locate the element interiorly, it may be advantageous insome circumstances to locate the element on the exterior surface of thespring or use the element to construct all or part of the helical coilspring portion of the guide wire.

In another embodiment, the shape memory alloy element is in the form ofa wire freely slidable within the helices of a tightly coiled spring. Inthis case, the wire may be previously selectively annealed at one ormore spaced portions along its length. As the memory alloy is heated toits transitional temperature, the alloy curves to its annealed shape andthus bends the otherwise straightly aligned coils into the desiredshape.

The guide wire may also consist only of a single strand of solid wirecomposed in part or entirely of shape memory alloy material, again withselectively applied shape memory characteristics. It will be understoodthat multiple curves generated at selected positions along the length ofthe wire may be used to both steer and/or anchor the guide wire.

In another embodiment, the guide wire comprises at least a pair ofelongated shape memory wires, freely slidable with respect to each otherbut loosely held together by a helical wrap, sleeve or the like. In thisembodiment, the shape memory members, or wires, are oriented so that onemember changes shape in a direction opposite to the shape assumed by theother member. Thus, after applying a transitional temperature heat toone member to effect one shape, it is possible to later modify orreverse the first shape by activating another member of the guide wireassembly which is oriented to change shape in a direction diametricallyopposed to the first member. In this way, the second member acts as anantagonist to the first member.

In each of the above embodiments, the memory alloy exerts greater forceto retain its annealed shape when its transitional temperature ismaintained. Thus, when the memory alloy is allowed to cool below itstransitional temperature, the force of its memory in a given shape isreduced. By utilizing this phenomena in conjunction with memory alloyantagonists, accurate movement of the tips or selected body portions ofalloy configured guide wires can be achieved. For example, if a tightlycoiled but overall straight length of guide wire is fitted with one ormore freely slidable memory alloy members, previously annealed to effectcurved shapes upon heating, then as the transitional temperature isreached and maintained, the whole assembly will bend to conform to theannealed shape. However, as the heat source is withdrawn and thetransitional temperature is not maintained, memory alloy force will bereduced so that, in properly dimensioned assemblies, the resilience ofthe coiled outer member will bend the inner alloy to a straightconfiguration. Conversely, if the tightly coiled helices aremechanically cold worked into curve or curves, and the memory alloy isannealed to effect a straight shape upon heating, then the guide wirewill exhibit a curved shape below the transitional temperature stateand, when brought to and maintained at the transitional temperature, theoverall shape of the guide wire will become straight. When cooled belowthe transitional temperature, the resilient force of the coiled outerguide wire will be greater than the reduced memory force exerted by thealloy wire, and thus the guide wire will return to its original curvedstate.

Accordingly, heat activated memory alloy components can be combined withnon-heat activated but structurally resilient materials to actantagonistically so that the tip or body of a guide wire can be steeredto and/or fro on command in any of several multiple directions. It isthus possible to steer, aim or anchor the tip and/or body of the guidewire in one direction and then another, as well to rotate the entireguide wire assembly 360° about its axis so as to be reversiblyomni-directional.

In addition to freely movable memory components of a guide wire, it isenvisioned that in some embodiments, one or more memory components canbe fastened or firmly attached to each other by welding, brazing, etc.so that upon heat activation of the memory components, certain desiredbending or shaping would occur as a consequence of the members not beingfully movable or slidable with respect to each other.

With respect to the manner in which the shape memory alloy materials areheated to the transitional temperature, various techniques may beemployed. For example, induction heating, application of radio frequency(RF) energy, and immersion heating by water or other suitable solution,are effective. In addition, body heat may also be relied upon to effectshape change. In such case, it will be appreciated that the compositionof the shape memory alloy material must be selected so that it has atransitional temperature at or just below body temperature.

Where induction heating is employed, the guide wire itself, any and allcomponents thereof, as well as the electrical wires employed to passcurrent through the guide wire, may be insulated by a non-conductivesleeve, coating, etc. to prevent current leakage outside the device.

Accordingly, the present invention involves the construction of animproved guide wire or the like, utilizing in whole or in part, shapememory alloy materials which enable accurate deflection of the guidewire to steer it to a desired location, with or without furthercooperation with a non-heat activated memory material.

Additional objects and advantages of the invention will become apparentfrom the detailed description and claims which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a through 1e illustrate tightly coiled spring guide wires whichincorporate shape memory alloy components in accordance with thisinvention;

FIGS. 2a and 2b illustrate a solid, single element guide wire composedentirely of a shape memory alloy in accordance with another embodimentof this invention;

FIGS. 3a and 3b illustrate guide wires comprising plural shape memoryalloy components in accordance with still another embodiment of thisinvention; and

FIG. 4 illustrates a rectangularly shaped memory alloy component for usewith spring guide wires in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1a through 1e, tightly coiled spring guide wires10 are disclosed which incorporate shape memory alloy components indifferent forms and in different locations in order to achieve anaccurately steerable guide wire. In FIG. 1a, the coiled spring guidewire 10, which may be stainless steel or other suitable material, isfitted at its distal tip 12 with a substantially straight wire component14 constructed of a shape memory alloy material that can be accuratelysteered or deflected in one plane as illustrated by the dotted linepositions, when subjected to heat. Heating may be achieved by applyingcurrent to the component 14 by electrical wires 16, 18 which areenclosed in a suitable cable 20 and connected to a control unit 22.Heating of component 14 above its transitional temperature will resultin deflection to a previously annealed shape, as indicated in phantom inFIG. 1.

The wires 16, 18 may be attached to the component 14 by any suitablemeans such as welding or brazing. It will be understood that the coiledspring itself could be utilized as the grounding wire, if it wereconstructed of a suitable electrically conductive material. Aspreviously described, however, various other heating techniques may beemployed which will enable component 14 to reach its transitionaltemperature, where it will assume its previously annealed shape toeffect steering of the spring guide wire 10. Body temperature, immersionheating, and RF heating are considered exemplary but not limiting.

In FIG. 1b, the coiled spring guide wire 10 is fitted with a shapememory alloy component 24 at a point intermediate its ends, andpreferably within the lumen of the spring, so that when heat is applied,the guide wire will bulge outwardly, as shown in phantom. It will beunderstood that the component 24 may also be attached to the exterior ofthe coiled spring guide wire. In either case, the component will beattached at one or both ends to individual coils of the spring, or atone or more points intermediate the ends of the component, but not alongits entire length, since some relative motion must be permitted betweenthe coils of the spring and the shape memory alloy component.

It will be appreciated that the coiled spring guide wires illustrated inFIGS. 1a, b and c may themselves be formed in part, or entirely, of ashape memory alloy, and annealed to assume one or more desired shapeswhen heated.

Turning now to FIG. 1c, a single, shape memory alloy wire 28 isillustrated running the full length of the coiled spring guide wire 10and freely slidable with respect thereto. In this embodiment, selectivesections of the wire, for example the tip 30, and one or moreintermediate portions 32, may be previously annealed to variously curvedshapes, whereas the remainder of the wire remains straight upon heating.Steering capability in this embodiment is enhanced since multiple curvesin various directions are possible.

FIG. 1d illustrates a discrete memory component 34 fitted into the lumenof the coiled spring guide wire 10, and specifically, in the distalregion thereof. The component 34 is mounted so that the alloy and thecoils are slidable relative to one another, in order to accommodate therespective motion of each during a bending phase, which is againillustrated in phantom.

In FIG. 1e, a memory component 36 is fitted within the coils of thespring guide wire 10 in a manner similar to that shown in FIG. 1d.However, in this embodiment, the distal end portion 38 of the coiledspring itself may be cold-worked into a substantially J-shape or othercurved configuration, with the shape memory alloy component 36 havingbeen previously annealed in a straight line configuration. Thus, theforce of the coils configured in the curved or substantially J-shape,will bend the memory alloy into a corresponding shape prior to theapplication of heat. However, when heat is applied to the memory alloyat the transitional temperature, and maintained, the shape memory alloycomponent 36 reverts to its straight annealed shape, overcoming theresilience of the coiled spring. When the heat is discontinued, and thememory alloy component 36 allowed to cool below its transitionaltemperature, the memory force is reduced whereby the resilience of thecoiled spring again predominates, and the original J-shaped curve isonce again achieved by reason of the coiled springs own mechanicalmemory. It will therefore be understood that the application of heat tothe memory alloy and the subsequent discontinuance of heat andconsequential cooling of the memory alloy below its transitionaltemperature is the operating principle by which guide wire steeringcapability may be effected in any desired direction and the reversethereof.

FIG. 2a illustrates a single, solid guide wire 40 comprised in itsentirety of a shape memory alloy material, wherein selected sections ofthe wire are previously annealed to various shapes while the remainderof the wire is annealed to a substantially straight line configuration.In this particular embodiment, the tip portion 42 is annealed to acurved shape, illustrated in phantom, and an intermediate section 44 isannealed to a sinusoidal shape to provide even greater steeringcapability.

FIG. 2b illustrates another single component, solid guide wire 46wherein a forward or distal end portion 48 is annealed to a multiplecurve, or deflection, configuration which enables the guide wire to besecurely anchored at the desired location, so that it is not readilydislodged by pulling or pushing forces exerted, for example, by anassociated catheter which is normally telescoped over the guide wireafter the guide wire is steered to its final, desired position.

In FIG. 3a, still another arrangement is illustrated wherein two wiremembers 50, 52 of memory alloy material are held together by one or moreplastic or metal sleeves 54 and/or ties 56. Members 54, 56 are free toslide longitudinally along the members 50, 52 which are also free toslide relative to each other to accommodate movement as required duringthe shaping or bending phase. In this example, the two wire members 50,52 are substantially straight but may be annealed with curves which are180° opposed as indicated by phantom positions A and B. It will thus beseen that the application of heat to member 50 will cause its deflectionin one plane, to position A, with member 50 bringing the second member52 along with it by reason of the presence of the one or more sleeves54, or ties 56. Upon the application of heat to the second member 52,the curve in member 50 can be straightened out or if desired pulled 180°in the opposite direction to position B, as it conforms to itsantagonist. In this fashion, a given bend or shape can be effected byheating one member and subsequently reversed, either to a straightconfiguration, or to a bend in the opposite direction by heating thesecond member. By combining two or more shape memory alloys, each havingannealed shapes, the sequential and selective heating of one or more ofthe alloys, coupled with controlled rotation of the guide wire, canresult in omni-directional and reversible steering as desired.

It will be understood that members 50, 52 may also be firmly attached toeach other by welding, brazing, etc. (as shown in phantom in FIG. 3a) inorder to obtain certain other desired bends or shapes which could not beachieved if the elements were freely slidable with respect to eachother.

FIG. 3b operates in substantially the same manner as FIG. 3a, exceptthat a group of four wire memory elements 58, 60, 62 and 64 are heldtogether by a helical wrap 66 of Kevlar™ or other suitable material.

FIG. 4 illustrates a shape memory alloy component 68 useable in all ofthe above described embodiments. The component 68 is formed as one ormore rectangular strips which may be preferable in certain applications.It will be understood, however, that this invention contemplatesvirtually any cross-sectional shape for the memory alloy including solidor hollow, round, oval, rectangular, square, triangular, etc.

It will be further understood that all of the above described guide wireconstructions may be associated with control means which can effectrotation of the guide wires about a full 360° to achieve reversible andomni-directional steering capability.

Also, as explained previously, other transitional temperature activatedmechanical memory materials can be utilized besides the above-mentionedtitanium-nickel, titanium-nickel cobalt, and titanium-copper alloys.While the above-mentioned alloys are especially advantageous since theanneal and shape change cycle may be repeated indefinitely as long asthe originally annealed temperature is not exceeded, thermoplastic orany other heat memory alloy materials may also be used.

Although preferred embodiments, uses and modifications of the inventionshave been depicted and disclosed, such description is to be consideredillustrative rather than limiting, particularly since those of ordinaryskill in the art would understand that various modifications and changesmay be made in the disclosed invention without departing from the spiritand scope of the claims which follow.

I claim:
 1. A steerable guide wire adapted to be inserted within thebody, and including shape memory alloy means for effecting accuratesteering or aiming of said within the body, said guide wire comprisingat least a pair of solid elongated shape memory wire members held insubstantial coaxial engagement with each other but so as to allowrelative sliding movement therebetween, and wherein one of said wiremembers is annealed to undergo a shape change in one direction uponapplication of heat, and another of said wire members is annealed toundergo a shape change in another direction upon application of heat,said guide wire being rotatable about 360° to thereby enable reversiblyomni-directional steering of said guide wire.
 2. A steerable guide wireas defined in claim 1 wherein said wire members are held together by atleast one element slidable with respect to said wire members.
 3. Asteerable guide wire as defined in claim 1 wherein said wire members areheld together by at least one tie member.
 4. A steerable guide wire asdefined in claim 1 wherein said wire members are held together by astrand helically wrapped about said wire members substantially along theentire length of said wire members.
 5. A steerable guide wire as definedin claim 1 wherein said guide wire is shaped and sized for use as avehicle to precede and position a catheter.
 6. A steerable guide wire asdefined in claim 1 wherein said guide wire is shaped and sized toprecede and to serve as a vehicle for positioning an angioplastycatheter.
 7. A steerable guide wire as defined in claim 1 wherein saidguide wire is shaped and sized for use as a vehicle to precede andposition an angiographic catheter.
 8. A steerable guide wire as definedin claim 1 and further including means to effect heating of said shapememory wire members.
 9. A steerable guide wire as defined in claim 8wherein said heat effecting means comprises induction heating.
 10. Asteerable guide wire as defined in claim 9 wherein said guide wire is atleast partially insulated with non-conductive material to preventcurrent leakage outside the guide wire.
 11. A steerable guide wire asdefined in claim 8 wherein said heat effecting means comprises bodytemperature.
 12. A steerable guide wire is defined in claim 8 whereinsaid heat effecting means comprises immersion heating.
 13. A steerableguide wire adapted to be inserted within the body, and including shapememory alloy means for effecting accurate steering or aiming of saidwithin the body, wherein said guide wire comprises at least a pair ofsolid elongated shape memory wire members fixedly secured to each otherto prevent relative movement therebetween, and wherein one of said wiremembers is annealed to undergo a shape change in one direction uponapplication of heat, and another of said wire members is annealed toundergo a shape change in another direction upon application of heat.14. A steerable guide wire as defined in claim 1 wherein said shapememory alloy means is a titanium-nickel alloy.
 15. A steerable guidewire as defined in claim 1 wherein said shape memory alloy means iscomprised of a heat settable plastic material.
 16. A steerable guidewire as defined in claim 1 wherein said shape memory alloy means is atitanium-nickel-cobalt alloy.
 17. A steerable guide wire as defined inclaim 1 wherein said shape memory alloy means is a titanium-copperalloy.